Container for framed pellicle

ABSTRACT

The invention provides an improvement in a pellicle container for containing a framed pellicle conventionally made from a plastic resin, which is mounted on a photolithographic photomask for dust-proof protection thereof. A serious problem in the plastic resin-made container is adsorption or deposition of organic matters emitted from the container body by or on the pellicle membrane during storage or transportation resulting in a decrease in the light transmission as well as accelerated degradation of the pellicle membrane to the light of an extremely short wavelength for patternwise exposure in the photolithography while this problem can be solved by the improvement of the invention according to which at least the surface layer of the container surfaces facing the space for containing the framed pellicle is formed from an inorganic material, e.g., metals, glass materials and ceramics, free from emission of any organic matters.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a container for a framedpellicle or, more particularly, to a container for containing a framedpellicle used for dust-proof protection of a photomask in thephotolithographic patterning works. In particular, the improvement ofthe invention is directed to the structure of a pellicle container forcontaining a framed pellicle used with an object of dust-proofprotection of a photomask in the patterning works in the manufacture offine and precision electronic devices including semiconductor devicessuch as LSIs and VLSIs and liquid crystal display panels.

[0002] Photolithographic patterning is a conventional and establishedtechnology in the manufacturing process of fine and precision electronicdevices including semiconductor devices such as LSIs and VLSIs andliquid crystal display panels. In the photolithographic patterningworks, the surface of the substrate for the device is patternwiseexposed to actinic rays such as ultraviolet light through apattern-bearing transparency called a photomask. It is very importanthere that the surface of the photomask is absolutely free from dustparticles deposited thereon because the quality of patterning is greatlyaffected adversely by the dust particles on the photomask due toabsorption, scattering and diffraction of the exposure light. In thisregard, photolithographic patterning works are conducted in a dust-freeatmosphere of a clean room although it is almost impossible to beabsolutely free from dust particles even in a clean room of the highestclass. A usual procedure therefore is that a framed pellicle fordust-proof protection is mounted on the photomask and the patterninglight-exposure is conducted through the transparent pellicle membrane ofthe framed pellicle.

[0003] When the patterning light-exposure is conducted through thepellicle membrane of a framed pellicle mounted on the photomask, dustparticles deposited on the surface of the pellicle membrane have noparticular adverse effects on the quality of patterning since theexposure light is focused not at the dust particles but at the photomaskwhich is at least several millimeters below the pellicle membrane.

[0004]FIG. 1 of the accompanying drawing illustrates a vertical crosssectional view of a typical framed pellicle 6 which is an integraldevice basically consisting of a square or circular frame 3, referred toas a pellicle frame, of a rigid material and a thin and highlytransparent film 1, referred to as a pellicle membrane, of a plasticresin spread over one end surface of the pellicle frame 3 and adhesivelybonded thereto in a slack-free fashion with intervention of an adhesivelayer 2 therebetween. The other end surface of the pellicle frame 3 isusually coated with a pressure-sensitive adhesive forming apressure-sensitive adhesive layer 4 in order to facilitate mounting ofthe framed pellicle 6 on the photomask with stability. The surface ofthe pressure-sensitive adhesive layer 4 is temporarily protected untiluse by attaching a releasable film or sheet 5.

[0005] The plastic resin forming the pellicle membrane 1 is usuallyselected from nitrocelluloses, cellulose acetates and fluorocarbonpolymers in view of their good mechanical strengths even in the form ofa thin films and high transparency to the exposure light. A glass plateis also proposed in place of the pellicle membrane 1 of a plastic resin.The rigid material forming the pellicle frame 3 is usually selected fromaluminum, stainless steel, polyethylene and the like. The pelliclemembrane 1 is adhesively bonded to one of the end surfaces of thepellicle frame 3 by using an adhesive 2 which can be an acrylicresin-based adhesive, epoxy resin-based adhesive or fluorocarbonresin-based adhesive according to the disclosure in U.S. Pat. No.4,861,402, Japanese Patent Publication No. 58-219023, Japanese PatentKokai No. 7-168345 and elsewhere. Alternatively, Japanese Patent KokaiNo. 58-219023 proposes a bonding method in which an organic solventhaving good dissolving power to the plastic resin of the pelliclemembrane 1 is applied to the end surface of the pellicle frame 3followed by partial drying and the pellicle membrane 1 is brought intocontact with the end surface of the pellicle frame still adequately wetwith the solvent.

[0006] The other end surface of the pellicle frame 3, i.e. the endsurface opposite to the pellicle membrane 1, is usually provided with apressure-sensitive adhesive layer 4 by coating with a suitablepressure-sensitive adhesive based on a polybutene resin, polyvinylacetate resin, acrylic resin or silicone resin. The surface of thepressure-sensitive adhesive layer 4 is temporarily protected until useof the framed pellicle 6 by attaching a releasable sheet or separator 5which is removed by peeling immediately before the framed pellicle 6freed from the releasable sheet 5 is mounted on the photomask by gentlypressing against the photomask. Needless to say, framed pellicles 6 withthe above mentioned releasable sheet 5 are transported and stored ascontained in a rigid container for a framed pellicle 6, which isconventionally formed from a plastic resin, in order to protect the sameuntil use against mechanical damages and contamination.

[0007] Turning now to the light for patternwise exposure through thepellicle membrane 1, it is a remarkable trend in recent years to be incompliance with the requirement toward a finer and finer resolution ofthe photolithographic pattern, the exposure light is under a continuousshift toward those of shorter and shorter wavelengths in order toaccomplish the high pattern resolution. For example, the g-line lightand l-line light having a wavelength of 436 nm and 365 nm, respectively,which were the major current of the exposure light, now have beenreplaced with the deep UV light of 248 nm wavelength from a KrF excimerlaser which in turn is under replacement with vacuum UV light of 193 nmwavelength from an ArF excimer laser. It is already foreseen that the UVlight of a still shorter wavelength of 158 nm such as the fluorineexcimer laser beams will be actually employed as the exposure light inphotolithographic patterning.

[0008] It has unexpectedly become apparent that a very serious problemmust be solved in order to conduct the patterning exposure inphotolithography by using the above mentioned extremely short-wavelengthlight as the patterning exposure light. Namely, it is unavoidable thatthe pellicle membrane 1 made from a plastic resin more or less adsorbsgaseous hydrocarbon compounds and moisture from the atmospheric air andthese adsorbates have an effect of decreasing the transmissivity of thepellicle membrane 1 to the exposure light. In addition, these adsorbedgases are activated by the laser irradiation to form initiation sitesfor the degradation reaction of the plastic resin of the pelliclemembrane 1 resulting in a decrease in the durability of the framedpellicle 6.

[0009] Since it is usual that the framed pellicles manufactured in aproduction line are each contained in a plastic-made container andstored for a considerable length of time before the product istransported to the users for actual service, a chance of highpossibility for contacting with the above mentioned contaminant gases isgiven during storage of the framed pellicles in containers. Namely,plastic resins forming the container always contain, though in a traceamount, various organic compounds such as the unpolymerized monomercompounds and organic solvents as the polymerization medium and theseorganic impurity matters are more or less emitted from the containerwalls to be adsorbed by the pellicle membrane 1 of the framed pellicle 6contained in the container and act adversely as described above.

SUMMARY OF THE INVENTION

[0010] The present invention accordingly has an object to provide, inorder to solve the above described problem, a container for a framedpellicle which is free from emission of any organic matters which mightbe adsorbed on the pellicle membrane of a framed pellicle contained inthe container for transportation and/or storage to exhibit the adverseeffects of decreasing the light-transmissivity and acceleration ofdegradation of the pellicle membrane.

[0011] Thus, the present invention provides an improvement in acontainer for a framed pellicle as an assembly of a container base and acovering mountable on the container base jointly to form an inside spacefor containing a framed pellicle, which improvement comprises forming atleast the surface layer of the container base and the covering facingthe inside space from an inorganic material selected from the groupconsisting of metals, alloys, glass materials and ceramic materials.

[0012] While the minimum requirement of the present invention is to formthe inner surface layer of the container from an inorganic material, itis optional that the whole bodies of the container base and the coveringare formed entirely from an inorganic material or that both of the innerand outer surface layers of the container are formed from an inorganicmaterial.

BRIEF DESCRIPTION OF THE DRAWING

[0013]FIG. 1 is a schematic vertical cross sectional view of a framedpellicle.

[0014]FIG. 2 is a schematic vertical cross sectional view of aninventive container formed entirely from an inorganic materialcontaining a framed pellicle therein.

[0015]FIG. 3 is a schematic vertical cross sectional view of aninventive container of which both of the inner and outer surface layersare formed from an inorganic material containing a framed pellicletherein.

[0016]FIG. 4 is a schematic vertical cross sectional view of aninventive container of which the inner surface layer only is formed froman inorganic material containing a framed pellicle therein.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] As is illustrated in FIG. 2, the container 7 of the presentinvention is an assembly composed of a container base 7A and a covering7B mountable on the container base 7A. When the covering 7B is mountedon the container base 7A in place, an inside space 7C is formed tocontain the framed pellicle 6.

[0018] The most characteristic feature of the inventive container 7 fora framed pellicle is that at least the surface layer of the container 7,i.e. container base 7A and covering 7B, facing the inside space 7C isformed from an inorganic material which can be a metal or alloy, glassmaterial or ceramic material. Examples of the metal and alloy suitablefor the purpose include aluminum, copper, iron and stainless steels. Thesurface of the layers of these metallic materials can be subjected to avariety of surface treatments with an object to improve stability andcorrosion resistance. For example, it is optional that the surface of analuminum layer is subjected to an anodization treatment to form anoxidized thin film thereon. The glass material is not particularlylimitative including fused silica glass. The ceramic material used hereis exemplified by silicon nitride, silicon carbide, zirconia, alumina,boron nitride and the like.

[0019] Instead of forming the entire body of the container 7 from theabove mentioned inorganic material as is illustrated in FIG. 2, it isoptional that the walls of the container have a composite layeredstructure consisting of a core 8A or 8B made from a conventional plasticresin and cladding layers 9, 10 of an inorganic material on the outerand inner surfaces, respectively, of the cores 8A, 8B as is illustratedin FIG. 3 by a vertical cross sectional view containing a framedpellicle 6 in the inside space. It is of course that the cladding layers10 of an inorganic material on the outer surface of the container baseand covering are not essential and can be omitted as is illustrated inFIG. 4 by a vertical cross sectional view containing a framed pellicle6. Namely, the inorganic cladding layer 10 is formed only on thesurfaces of the container base 8A and covering 8B of a plastic resinfacing the inside space 7C to contain the framed pellicle 6.

[0020] The inorganic cladding layers 10 on the inner surfaces of thecores 8A, 8B of the container should desirably have a thickness of atleast 0.1 μm. When the thickness is too small, the inorganic claddinglayers are eventually subject to the formation of cracks or fissures sothat emission of organic contaminant gases from the cores 8A, 8B of aplastic resin cannot be completely prevented. The method for forming theinorganic cladding layers 10 on the surfaces of the cores 8A, 8B is notparticularly limitative depending on the kind of the inorganic materialsand desired thickness of the cladding layers 10. For example, theinorganic cladding layers 10 can be formed by the vacuum vapordeposition method or, alternatively, by adhesively bonding a thin sheetof the inorganic material by using an adhesive.

[0021] Following is a description of the present invention in moredetail by way of Examples and a Comparative Example making reference tothe accompanying drawing, which is preceded by the description of thepreparation procedure of framed pellicles to be contained in thecontainer.

[0022] Thus, a framed pellicle 6A was prepared by adhesively bonding aglass sheet of 1 mm thickness to serve as the pellicle membrane onto oneof the end surfaces of an aluminum-made pellicle frame coated with asilicone resin-based adhesive while the other end surface of thepellicle frame was coated with a silicone resin-based pressure-sensitiveadhesive in a thickness of 0.5 mm and the pressure-sensitive adhesivelayer was protected by attaching a releasable film.

[0023] Another framed pellicle 6B was prepared in about the same manneras above excepting for the replacement of the 1 mm thick glass sheetwith a 0.5 μm thick film of a fluorocarbon resin which was spread overand adhesively bonded to the adhesive-coated end surface of the pellicleframe in a slack-free fashion.

[0024] The pellicle membranes of the framed pellicles 6A, 6B hadtransmissions of 80% and 90%, respectively, to the fluorine excimerlaser beams of 158 nm wavelength. In the Examples and ComparativeExample shown below, these framed pellicles were kept for a length oftime in several different pellicle containers and measurements were madefor the transmission of the pellicle membranes after storage to thefluorine excimer laser beams.

EXAMPLE 1

[0025] The framed pellicles 6A, 6B prepared as above were each kept in apellicle container entirely made of aluminum for 1 month at roomtemperature. The framed pellicles 6A, 6B taken out of the respectivepellicle containers were subjected to the transmission measurement ofthe fluorine excimer laser beams to give values of 80% and 90%,respectively, showing no decrease as a consequence of storage.

EXAMPLE 2

[0026] The experimental procedure was substantially the same as inExample 1 excepting for the replacement of the aluminum-made pelliclecontainers with containers entirely made from fused silica glass. Thetransmission values of the pellicle membranes of the framed pellicles6A, 6B after 1 month storage therein were 80% and 90%, respectively, tothe fluorine excimer laser beams showing no decrease as a consequence ofstorage.

EXAMPLE 3

[0027] The experimental procedure was substantially the same as inExample 1 excepting for the replacement of the aluminum-made pelliclecontainers with containers made from an ABS resin and provided with a0.1 μm thick cladding layers of aluminum formed by the method of vacuumvapor deposition on the overall surfaces of the container base andcovering. The transmission values of the pellicle membranes of theframed pellicles 6A, 6B after 1 month storage therein were 80% and 90%,respectively, to the fluorine excimer laser beams showing no decrease asa consequence of storage.

EXAMPLE 4

[0028] The experimental procedure was substantially the same as inExample 3 except that the 0.1 μm thick cladding layers of aluminum wereformed only on the inward surfaces of the ABS resin-made container baseand covering facing the inside space for containing the framed pellicle.The transmission values of the pellicle membranes of the framedpellicles 6A, 6B after 1 month storage therein were 80% and 90%,respectively, to the fluorine excimer laser beams showing no decrease asa consequence of storage.

EXAMPLE 5

[0029] The experimental procedure was substantially the same as inExample 3 except that the cladding layers on the surfaces of thecontainer base and covering had a double-layered structure consisting ofa 0.5 μm thick undercladding layer of aluminum and 0.5 μm thick topcladding layer of boron nitride each formed by the method of vacuumvapor deposition. The transmission values of the pellicle membranes ofthe framed pellicles 6A, 6B after 1 month storage therein were 80% and90%, respectively, to the fluorine excimer laser beams showing nodecrease as a consequence of storage.

Comparative Example

[0030] The experimental procedure was substantially the same as inExample 1 excepting for the replacement of the aluminum-made pelliclecontainers with containers made from a polymethyl methacrylate resinhaving no inorganic cladding layers thereon. The transmission values ofthe pellicle membranes of the framed pellicles 6A, 6B after 1 monthstorage therein were 47% and 50%, respectively, to the fluorine excimerlaser beams showing remarkable decreases as a consequence of storage.

What is claimed is:
 1. In a container for a framed pellicle as anassembly of a container base and a covering mountable on the containerbase jointly to form an inside space for containing a framed pellicle,the improvement which comprises forming at least the surface layer ofthe container base and the covering facing the inside space from aninorganic material selected from the group consisting of metals oralloys, glass materials and ceramic materials to form a cladding layer.2. The improvement as claimed in claim 1 in which the container base andthe covering of the container are entirely formed from the inorganicmaterial.
 3. The improvement as claimed in claim 1 in which the claddinglayer of an inorganic material is formed only on the surfaces of thecontainer base and the covering made from a plasyic resin facing theinside space.
 4. The improvement as claimed in claim 1 in which thecladding layer of an inorganic material is formed both on the surfacesof the container base and the covering made from a plastic resin facingthe inside space and on the outwardly facing surfaces thereof.
 5. Theimprovement as claimed in claim 1 in which the cladding layer of aninorganic material has a thickness of at least 0.1 μm.
 6. Theimprovement as claimed in claim 1 in which the metal or alloy formingthe cladding layer is selected from the group consisting of aluminum,copper, iron and stainless steels.
 7. The improvement as claimed inclaim 1 in which the ceramic material forming the cladding layer isselected from the group consisting of silicon nitride, silicon carbide,zirconia, alumina and boron nitride.